Relative to the link between extreme left and extreme right, the report explains that the moderate right is losing a similar portion of the votes regardless of the level of abstention in the districts, while the left is losing more in districts where abstention is high. For me, this is again evidence of the focal point played by the FN as a protest vote.
Indeed, they have more: there were European elections in 2009 and local elections in 2010. The report reports an interesting report:
The FN attracted numerous abstainer (16 % of the 2009 abstainers voted FN [in 2010]), but if got electors everywhere: 15% of "souverainistes" electors(...), 6% of those who had turned to the "Front De Gauche", 4% of those who voted for the extreme left(...)